1. Field of the Invention
The present invention relates to a semiconductor film and a method for manufacturing the semiconductor film. The present invention relates to a power storage device.
Note that the power storage device refers to all elements and devices which have a function of storing power.
2. Description of the Related Art
In recent years, high-performance power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air cells have been developed.
An electrode for the power storage device is manufactured by providing an active material over a surface of a current collector. As the active material, a material such as carbon or silicon, which can store and release ions serving as carriers, is used. For example, silicon or phosphorus-doped silicon has higher theoretical capacity than carbon and is advantageous in increasing the capacity of a power storage device (e.g., Patent Document 1).
On the other hand, a needle-like microstructure is known, which is expected to be applied to a power storage device including an ion-transferring secondary battery (e.g., a lithium ion battery), with its external characteristics.
As the needle-like silicon microstructure, a silicon nanoneedle formed by a vapor-liquid-solid (VLS) growth method is known (see Patent Document 2). A silicon nanoneedle is a single crystal needle-like structure obtained from a single crystal substrate; for example, the diameter of an end portion is 300 nm or less and the length is approximately 90 μm or less.